Conjugation (or mating) in Paramecium (as in numerous other species of protozoa and bacteria) occurs between complementary cells during special periods of reactivity. The interaction between reactive cells of opposite mating type shows an unusually high degree of specificity. When cells of opposite (complementary) mating type are mixed in culture, they adhere to one another on contact forming clumps containing as many as twenty cells. The initial agglutination of reactive cells involves only the cilia of the animals and only those cilia which are located along the oral surface. Within minutes of contact, the initial agglutination reaction is followed by pairing of complementary cells which separate from the initial clump. The complementary pairs undergo a fusion of their membranes along the oral surface which is followed by a reciprocal exchange of gametic nuclei and eventually mitosis. The process of specific cell agglutination and the subsequent events leading to mitosis are reminiscent of the biological actions associated with another class of agglutinus - the lectins. The project outlined in this report is designed to isolate and chemically characterize the substance(s) involved in the highly specific cell recognition and agglutination reaction referred to as mating.